In steam generators heating surface is normally disposed in the vertical rear pass leading from the furnace as a means of absorbing heat from the combustion gases passing therethrough. This surface comprises serpentine tubes through which the fluid being heated progresses either upward or downward therethrough, while either being superheated or reheated, or in the case of economizer surface the water is heated.
In small steam generators, these serpentine elements are end supported, while in larger units the supported span is too large, causing too much deflection and stress. Thus vertical support tubes are run through the rear pass on which the horizontal tube runs are supported. Some tube runs expand more than others, due to the difference in temperature of the fluid passing therethrough, or the difference in gas temperatures between the upper and lower gas pass locations. To avoid problems of over-stress caused by unequal thermal growth, it is necessary to support the horizontal tube runs from the vertical support tubes in a manner that will permit relative movement between both the horizontal and vertical tubes, and between adjacent horizontal tube runs.